Indirect economic impact of landslide hazards by disruption to national road transportation networks; Scotland, United Kingdom

Indirect economic impact of landslide hazards by disruption to national road transportation networks; Scotland, United Kingdo

Characterising regional landslide initiation thresholds in Scotland, UK using NIMROD c-band precipitation radar and the BGS National Landslide Database

Characterising regional landslide initiation thresholds in Scotland, UK using NIMROD c-band precipitation radar and the BGS National Landslide Databas

Evaluating 21st century projections of anticyclonic weather frequency and persistence over the British Isles

Evaluating 21st century projections of anticyclonic weather frequency and persistence over the British Isle

Rainfall thresholds and susceptibility mapping for shallow landslides and debris flows in Scotland [poster]

Shallow translational slides and debris flows (hereafter ‘landslides’) pose a significant threat to life and cause sig- nificant annual economic impacts (e.g. by damage and disruption of infrastructure). The focus of this research is on the definition of objective rainfall thresholds using a weather radar system and landslide susceptibility mapping. In the study area Scotland, an inventory of 75 known landslides was used for the period 2003 to 2016. First, the effect of using different rain records (i.e. time series length) on two threshold selection techniques in receiver operating characteristic (ROC) analysis was evaluated. The results show that thresholds selected by ‘Threat Score’ (min- imising false alarms) are sensitive to rain record length and which is not routinely considered, whereas thresholds selected using ‘Optimal Point’ (minimising failed alarms) are not; therefore these may be suited to establishing lower limit thresholds and be of interest to those developing early warning systems. Robust thresholds are found for combinations of normalised rain duration and accumulation at 1 and 12 day’s antecedence respectively; these are normalised using the rainy-day normal and an equivalent measure for rain intensity. This research indicates that, in Scotland, rain accumulation provides a better indicator than rain intensity and that landslides may be gen- erated by threshold conditions lower than previously thought. Second, a landslide susceptibility map is constructed using a cross-validated logistic regression model. A novel element of the approach is that landslide susceptibility is calculated for individual hillslope sections. The developed thresholds and susceptibility map are combined to assess potential hazards and impacts posed to the national highway network in Scotland

Attributes of the models.

<p>Grey shading indicates the variable changed in each group of models. See Section 3 for a discussion of the conceptual framework, which outlines the different parts that comprise the models. SI and WT in column 1 refer to the ‘Stochastic Instability’ and ‘Waiting Time’ models, respectively. Models 1–5 are in Appendix A. The distribution shapes each model can produce are described in sections where they are developed, and acceptable approximations to observations are log-normal, gamma or exponential above the mode.</p

Framework for the statistical models.

<p>Cross-hatched area in a) is a meso-scale (~10s-100s km) ‘patch’ of deformable or erodible subglacial material subject to conditions conducive to a flow set of bedforms arising. b) and c) are barcode style strips for the waiting time (WT) [M10] and stochastic instability (SI) [M7] models. The strips represent the size evolution through time for one of the bedforms <i>j</i> in a). Specifically, the bands represent alternating `local’ (~0.1–1 km) conditions affecting <i>H</i>; grey is growth, and white is shrinking or inactivity. <i>k</i> and <i>kH</i> indicate growth rate (i.e., Eqs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159489#pone.0159489.e001" target="_blank">1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159489#pone.0159489.e004" target="_blank">4</a>). Rapid fluctuations in c) are omitted for visual clarity, analogous to a time-series recorded at low temporal resolution.</p

Illustration of how, conceptually, unequal rates of growth and shrinking may be decomposed into components.

<p>The components represent: i) oscillation around the centre of a distribution of the logarithm of sizes; and ii) drift of the distribution.</p

Pdfs for models with deterministic growth and variable initial topography a) linear growth [M2] b) exponential growth [M3].

<p>Initial <i>H</i> distribution <i>H</i>_i (grey, dashed line) changes to the final one <i>H</i>_f (black outline) as time progresses. Dotted lines are an arbitrary function. Cases shown are where smallest <i>H</i>_i is zero; <i>a</i> = 0.</p

Visualisation of the relationship between a random walk, a Wiener process, and the evolving log-normal size-frequency distribution expected of bedforms in the SI model [M7].

<p>a) Probabilities for the number of discrete steps taken in a random walk (grey circles) are distributed binomially. From Wiener’s work whatever small step length is chosen these are well approximated by normal distribution (black line) of μ = 0 and σ² = <i>t</i> i.e., net time spent growing is a normally distributed random variable. If <i>H</i> ∝ exp(<i>t</i>_<i>N</i>) this defines a log-normal distribution for <i>H</i>. b) Height distributions evolving through the SI model [M7] as time increases for some illustrative constants.</p

Conceptualisation of how flow-sets of bedforms grow.

<p>a) Cross-hatched area is a meso-scale flow-set (~10–100 km) or `patch’ of deformable or erodible subglacial material subjected to conditions conducive to a flow set of bedforms arising in locations illustrated by black dots. Within this, bedforms from 1 to <i>j</i>, where <i>j</i> is any integer, change in amplitude through erosion, deposition, or redistribution. b) A potential, illustrative, sequence of growth for one bedform (number <i>j</i>) through time (dashed line), accompanied by selected silhouettes representing vertical cross-sections; a shrinking rate of zero (i.e., stasis) is valid within the illustration.</p